1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive that provides for serial interface amplitude selection in an unknown interconnect environment.
2. Description of the Prior Art and Related Information
Today, computers are routinely used both at work and in the home. Computers advantageously enable file sharing, the creation of electronic documents, the use of application specific software, and access to information and electronic commerce through the Internet and other computer networks. Typically, each computer has a storage peripheral, such as a disk drive (e.g., a hard disk drive).
Disk drives and other sorts of devices are typically connected to a host computer through a host interface connector for the transfer of commands, status and data. For example, the host computer accesses the disk drive and reads data from the disk drive and/or saves data to the disk drive. The host computer is typically connected to a disk drive or a device through a cable connection or a PCB connection. This connection is generally termed an “interconnect”. For compatibility, the connectors and interface protocol are typically standardized. Accordingly, the cable and connectors need to comply with the same interface standard.
In the past, the host computer has typically been connected to an external storage device, such as a hard disk drive, by a parallel interface. The most common parallel interface is the Parallel Advanced Technology Attachment/Integrated Drive Electronics (PATA/IDE) interface.
Today, disk drives and host computers are being designed to comply with newer faster standards that operate in a serial fashion. Examples of these newer serial standards include the Serial Advanced Technology Attachment (SATA) standard and the Serial Attached SCSI (SAS) standard. Both the SATA and SAS standards define various specifications for SATA and SAS compliant connectors and cables, along with various protocols for SATA and SAS devices, respectively.
The mixing of host computers and disk drives that operate utilizing different serial interface standards, such as SATA and SAS, is generally prohibited. Actual connector differences are often used as a mechanism to prevent such incompatible connections. SAS devices, however, often allow SATA devices to be attached. But, this can lead to signaling incompatibilities, and poor or even inoperable operating conditions.
Presently, there is no way to know if a device's signal amplitude (e.g., host computer or disk drive) is low due to the fact that it was attenuated by the interconnect, or because it was transmitted at a lower amplitude by a different standards-defined device type or a device configured for a different type of operating environment. Different amplitudes are typically pre-determined for different uses of a disk drive. For example, disk drives that are to be used internally (e.g., internal environment) typically have low amplitudes and operate at high frequencies and communicate over relatively short interconnects, whereas disk drives that are to be used externally (e.g., external environment—as part of an enterprise operation) typically operate at a high amplitude with lower frequency and communicate over relatively long interconnects.
In SATA and SAS serial devices, there are different signal amplitude specifications for various modes of operation. For example, there are internal signaling modes, high-loss motherboard signaling modes, and externally connected modes. In addition, there are specification differences between SATA and SAS.
As previously discussed, one particular problem is that a disk drive connected to a host computer does not know whether a low amplitude signal received from a host computer is the result of attenuation or a low transmission strength. Currently the SATA specification attempts to resolve the differences between internal and external environments by requiring that different connectors be used for internal and external connections. Thus, the SATA standard proposes mechanical interlocks to assure compatible devices. However, it is very simple to plug a disk drive into an incorrect connector by the use of a modified cable or adaptor. To complicate the problem, SAS devices allow for direct connection to SATA devices.
Unfortunately, there is presently no way, other than by the host computer and disk drive informing each other of their capabilities, to determine system compatibility. However, this requires that the host computer and disk drive connect to one another and directly inquire about each other's capabilities by some sort of interface protocol including identification commands and/or other status reporting. This presumes that communication is already possible.
However, as previously discussed, due to different standards-defined device types and different environment configurations, the host computer and the disk drive may not be able to communicate with one another to begin with, and even if they are able to communicate with one another, the communication may be unreliable. Further, there is no way to determine whether a low signal amplitude being received by a disk drive is due to the fact that the signal is being transmitted at a low amplitude or whether it is due to the fact that there is a lossy connection in the interconnect between the disk drive and the host computer.